7.1.24 W: Specify Warning Level/Map Width
The -Wnum option can be used to set the warning
level, in the range -9 to 9, or the width of the map file, for values of
num >= 10.
-W9 will suppress all warning messages.
-W0 is the default. Setting the warning level to -9
(-W-9) will give the most comprehensive warning messages.